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A New Chapter for MagicMirror: The Community Takes the Lead
Read the statement by Michael Teeuw here.

AHT20 Humidity + Temperature Sensor

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  • R Offline
    rkorell @JohnGalt
    last edited by rkorell Apr 16, 2025, 9:58 AM Apr 16, 2025, 9:55 AM

    the python script you are looking for is bme280.py

    #!/usr/bin/python
    #--------------------------------------
    #    ___  ___  _ ____
    #   / _ \/ _ \(_) __/__  __ __
    #  / , _/ ___/ /\ \/ _ \/ // /
    # /_/|_/_/  /_/___/ .__/\_, /
    #                /_/   /___/
    #
    #           bme280.py
    #  Read data from a digital pressure sensor.
    #
    #  Official datasheet available from :
    #  https://www.bosch-sensortec.com/bst/products/all_products/bme280
    #
    # Author : Matt Hawkins
    # Date   : 21/01/2018
    #
    # https://www.raspberrypi-spy.co.uk/
    #
    #--------------------------------------
    import smbus
    import sys
    import time
    from ctypes import c_short
    from ctypes import c_byte
    from ctypes import c_ubyte
    
    DEVICE = 0x76 # Default device I2C address
    
    try: #override device address like '0x77'
        DEVICE = int(sys.argv[1], 16)
    except:
        pass
    
    bus = smbus.SMBus(1) # Rev 2 Pi, Pi 2 & Pi 3 uses bus 1
                         # Rev 1 Pi uses bus 0
    
    def getShort(data, index):
      # return two bytes from data as a signed 16-bit value
      return c_short((data[index+1] << 8) + data[index]).value
    
    def getUShort(data, index):
      # return two bytes from data as an unsigned 16-bit value
      return (data[index+1] << 8) + data[index]
    
    def getChar(data,index):
      # return one byte from data as a signed char
      result = data[index]
      if result > 127:
        result -= 256
      return result
    
    def getUChar(data,index):
      # return one byte from data as an unsigned char
      result =  data[index] & 0xFF
      return result
    
    def readBME280ID(addr=DEVICE):
      # Chip ID Register Address
      REG_ID     = 0xD0
      (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
      return (chip_id, chip_version)
    
    def readBME280All(addr=DEVICE):
      # Register Addresses
      REG_DATA = 0xF7
      REG_CONTROL = 0xF4
      REG_CONFIG  = 0xF5
    
      REG_CONTROL_HUM = 0xF2
      REG_HUM_MSB = 0xFD
      REG_HUM_LSB = 0xFE
    
      # Oversample setting - page 27
      OVERSAMPLE_TEMP = 2
      OVERSAMPLE_PRES = 2
      MODE = 1
    
      # Oversample setting for humidity register - page 26
      OVERSAMPLE_HUM = 2
      bus.write_byte_data(addr, REG_CONTROL_HUM, OVERSAMPLE_HUM)
    
      control = OVERSAMPLE_TEMP<<5 | OVERSAMPLE_PRES<<2 | MODE
      bus.write_byte_data(addr, REG_CONTROL, control)
    
      # Read blocks of calibration data from EEPROM
      # See Page 22 data sheet
      cal1 = bus.read_i2c_block_data(addr, 0x88, 24)
      cal2 = bus.read_i2c_block_data(addr, 0xA1, 1)
      cal3 = bus.read_i2c_block_data(addr, 0xE1, 7)
    
      # Convert byte data to word values
      dig_T1 = getUShort(cal1, 0)
      dig_T2 = getShort(cal1, 2)
      dig_T3 = getShort(cal1, 4)
    
      dig_P1 = getUShort(cal1, 6)
      dig_P2 = getShort(cal1, 8)
      dig_P3 = getShort(cal1, 10)
      dig_P4 = getShort(cal1, 12)
      dig_P5 = getShort(cal1, 14)
      dig_P6 = getShort(cal1, 16)
      dig_P7 = getShort(cal1, 18)
      dig_P8 = getShort(cal1, 20)
      dig_P9 = getShort(cal1, 22)
    
      dig_H1 = getUChar(cal2, 0)
      dig_H2 = getShort(cal3, 0)
      dig_H3 = getUChar(cal3, 2)
    
      dig_H4 = getChar(cal3, 3)
      dig_H4 = (dig_H4 << 24) >> 20
      dig_H4 = dig_H4 | (getChar(cal3, 4) & 0x0F)
    
      dig_H5 = getChar(cal3, 5)
      dig_H5 = (dig_H5 << 24) >> 20
      dig_H5 = dig_H5 | (getUChar(cal3, 4) >> 4 & 0x0F)
    
      dig_H6 = getChar(cal3, 6)
    
      # Wait in ms (Datasheet Appendix B: Measurement time and current calculation)
      wait_time = 1.25 + (2.3 * OVERSAMPLE_TEMP) + ((2.3 * OVERSAMPLE_PRES) + 0.575) + ((2.3 * OVERSAMPLE_HUM)+0.575)
      time.sleep(wait_time/1000)  # Wait the required time  
    
      # Read temperature/pressure/humidity
      data = bus.read_i2c_block_data(addr, REG_DATA, 8)
      pres_raw = (data[0] << 12) | (data[1] << 4) | (data[2] >> 4)
      temp_raw = (data[3] << 12) | (data[4] << 4) | (data[5] >> 4)
      hum_raw = (data[6] << 8) | data[7]
    
      #Refine temperature
      var1 = ((((temp_raw>>3)-(dig_T1<<1)))*(dig_T2)) >> 11
      var2 = (((((temp_raw>>4) - (dig_T1)) * ((temp_raw>>4) - (dig_T1))) >> 12) * (dig_T3)) >> 14
      t_fine = var1+var2
      temperature = float(((t_fine * 5) + 128) >> 8);
    
      # Refine pressure and adjust for temperature
      var1 = t_fine / 2.0 - 64000.0
      var2 = var1 * var1 * dig_P6 / 32768.0
      var2 = var2 + var1 * dig_P5 * 2.0
      var2 = var2 / 4.0 + dig_P4 * 65536.0
      var1 = (dig_P3 * var1 * var1 / 524288.0 + dig_P2 * var1) / 524288.0
      var1 = (1.0 + var1 / 32768.0) * dig_P1
      if var1 == 0:
        pressure=0
      else:
        pressure = 1048576.0 - pres_raw
        pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
        var1 = dig_P9 * pressure * pressure / 2147483648.0
        var2 = pressure * dig_P8 / 32768.0
        pressure = pressure + (var1 + var2 + dig_P7) / 16.0
    
      # Refine humidity
      humidity = t_fine - 76800.0
      humidity = (hum_raw - (dig_H4 * 64.0 + dig_H5 / 16384.0 * humidity)) * (dig_H2 / 65536.0 * (1.0 + dig_H6 / 67108864.0 * humidity * (1.0 + dig_H3 / 67108864.0 * humidity)))
      humidity = humidity * (1.0 - dig_H1 * humidity / 524288.0)
      if humidity > 100:
        humidity = 100
      elif humidity < 0:
        humidity = 0
    
      return temperature/100.0,pressure/100.0,humidity
    
    def main():
    
      # (chip_id, chip_version) = readBME280ID()
      # print("Chip ID     :", chip_id)
      # print("Version     :", chip_version)
    
      temperature,pressure,humidity = readBME280All()
    
      print(round(temperature,1),round(humidity,1),round(pressure,1))
    
    if __name__=="__main__":
       main()
    

    @JohnGalt said in AHT20 Humidity + Temperature Sensor:

    Remote I/O error

    The given error seems to by not a program but an I/O problem.
    I’m not familiar with this sensor so I do not know how to connect and - most important - how to figure out the right “deviceAddress” - it seems that there is the error located.

    Either the address isn’t the correct one or the IO channel is somehow broken.
    For the latter came in my mind: if this is a I2C conected device - do you have enabled I2C on your Raspi?

    I’ve tried to “understand” what happens in the python script above as well as in the C-exmaple program on the Bosch product page for bme280 sensor, but didn’t got it…

    Regards,
    Ralf

    R J 3 Replies Last reply Apr 16, 2025, 10:35 AM Reply Quote 0
    • R Offline
      rkorell @rkorell
      last edited by rkorell Apr 16, 2025, 10:38 AM Apr 16, 2025, 10:35 AM

      @JohnGalt
      just seen while re-reading my last posting:

      nodehelper.js (the part of the module which is communicating with the python program and so with the sensor) is calling python3 :

      exec(`python3 ./modules/MMM-BME280/bme280.py ${deviceAddr}`, (error, stdout) => {
      

      but the python script itself is referencing python 2 (see above post, source code of bme280.py, 1st line:

      #!/usr/bin/python
      

      I guess this must match and doesn’t …
      So may this is the cause of your problems.

      And if this is true it is may really hard to get this working because you may run in several incompatibilities and library-conflicts …

      Regards,
      Ralf

      1 Reply Last reply Reply Quote 0
      • J Offline
        JohnGalt @sdetweil
        last edited by Apr 16, 2025, 9:47 PM

        @sdetweil – Thanks, Sam. It looks like I intended to send bme280.py but actually copied MMM-BME280.js. I see below where Ralf did post it, so I will look at that, too.

        1 Reply Last reply Reply Quote 1
        • J Offline
          JohnGalt @rkorell
          last edited by Apr 16, 2025, 9:57 PM

          @rkorell – Hi Ralf:

          Yes, I2C is enabled and functioning. There is a test script that does return current temperature and humidity:
          Invoking “python AHT20_test.py” does launch this script (Note - I launch from the terminal using ‘python’, not ‘python3’, telling me the system is indeed defaulting to python3):

          # SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
          # SPDX-License-Identifier: MIT
          
          """
          Basic `AHTx0` example test
          """
          
          import time
          import board
          import adafruit_ahtx0
          
          # Create sensor object, communicating over the board's default I2C bus
          i2c = board.I2C()  # uses board.SCL and board.SDA
          # i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
          sensor = adafruit_ahtx0.AHTx0(i2c)
          
          while True:
              print("\nTemperature: %0.1f C" % sensor.temperature)
              print("Humidity: %0.1f %%" % sensor.relative_humidity)
              time.sleep(2)
          
          1 Reply Last reply Reply Quote 0
          • J Offline
            JohnGalt @rkorell
            last edited by Apr 17, 2025, 1:01 AM

            @rkorell + @sdetweil - Thanks for the support. I think I have fixed this for myself by adapting an existing module (“MMM-Temperature”, // https://github.com/Tom-Hirschberger/MMM-Temperature).

            That module calls scripts for various sensors to capture the data. I was able to adapt an existing script for use with this sensor, so I think I am good for now.

            R 1 Reply Last reply Apr 17, 2025, 6:25 AM Reply Quote 2
            • R Offline
              rkorell @JohnGalt
              last edited by Apr 17, 2025, 6:25 AM

              @JohnGalt cool.
              congratulations.
              It’s may be worth to show the community what you have done?

              Regards,
              Ralf

              J 1 Reply Last reply Apr 17, 2025, 4:24 PM Reply Quote 0
              • J Offline
                JohnGalt @rkorell
                last edited by Apr 17, 2025, 4:24 PM

                @rkorell Yes, I can describe how I arrived at a resolution for my particular problem - which was to replace DHTxx sensors with the more accurate AHT20 temperature and humidity sensors.

                Caveat: I do not necessarily recommend this for the average person though, because I did not find Magic Mirror modules that natively support this sensor, and as a result had to make changes outside of the config.js and custom.css files. As usual, this puts me at risk of something breaking when the module is updated.

                The module being used (MMM-Temperature - found at https://github.com/Tom-Hirschberger/MMM-Temperature) utilizes python scripts to capture the data from the sensor. While the module is quite complete, with script support for many sensors, I did create a new script in order to use this particular sensor.

                The sensor is supported by Adafruit (https://learn.adafruit.com/adafruit-aht20/python-circuitpython), with instructions to install various adafruit libraries including adafruit-ahtx0 (sudo pip3 install adafruit-circuitpython-ahtx0).

                Using those libraries, your script needs to include the following instructions:

                import board
                import adafruit_ahtx0
                sensor = adafruit_ahtx0.AHTx0(board.I2C())
                

                One of the existing scripts supports I2C sensors using the Adafruit libraries, so it looked like a good candidate to use as a model. See htu21:

                #!/usr/bin/env python3
                #pip3 install adafruit-circuitpython-htu21d
                import board
                from adafruit_htu21d import HTU21D
                import json
                
                result = {}
                try:
                    # Create sensor object, communicating over the board's default I2C bus
                    i2c = board.I2C()  # uses board.SCL and board.SDA
                    sensor = HTU21D(i2c)
                    result["temperature_c"] = sensor.temperature
                    result["humidity"] = sensor.relative_humidity
                    result["temperature_f"] = (result["temperature_c"]*1.8) + 32
                    result["error"] = False
                except:
                    result["temperature_c"] = 0.0
                    result["humidity"] = 0.0
                    result["temperature_f"] = (result["temperature_c"]*1.8) + 32
                    result["error"] = True
                
                print(json.dumps(result))
                

                My resulting script is aht20:

                #!/usr/bin/env python3
                # aht20: Modeled on htu21 
                # pip3 install adafruit-circuitpython-htu21d
                # pip3 install adafruit-circuitpython-ahtx0
                import board
                import adafruit_ahtx0
                import json
                
                result = {}
                try:
                    # Create sensor object, communicating over the board's default I2C bus
                    i2c = board.I2C()  # uses board.SCL and board.SDA
                    # sensor = HTU21D(i2c)
                    sensor = adafruit_ahtx0.AHTx0(board.I2C())
                    result["temperature_c"] = sensor.temperature
                    result["humidity"] = sensor.relative_humidity
                    result["temperature_f"] = (result["temperature_c"]*1.8) + 32
                    result["error"] = False
                except:
                    result["temperature_c"] = 0.0
                    result["humidity"] = 0.0
                    result["temperature_f"] = (result["temperature_c"]*1.8) + 32
                    result["error"] = True
                
                print(json.dumps(result))
                

                This module is now displaying the temperature and humidity from the sensor directly connected it it. Now all I have to do is figure out the complicated css and get it to look like the other modules on my Magic Mirror.

                Barring any objections, I will mark this as solved.

                S R 2 Replies Last reply Apr 17, 2025, 4:34 PM Reply Quote 1
                • S Offline
                  sdetweil @JohnGalt
                  last edited by Apr 17, 2025, 4:34 PM

                  @JohnGalt css, use the developers window

                  see the second link in my signature below

                  Sam

                  How to add modules

                  learning how to use browser developers window for css changes

                  J 1 Reply Last reply Apr 17, 2025, 4:47 PM Reply Quote 0
                  • R Offline
                    rkorell @JohnGalt
                    last edited by rkorell Apr 17, 2025, 4:34 PM Apr 17, 2025, 4:34 PM

                    @JohnGalt Really COOL!
                    Thanks for sharing!
                    Ralf

                    J 1 Reply Last reply Apr 17, 2025, 4:47 PM Reply Quote 0
                    • J Offline
                      JohnGalt @sdetweil
                      last edited by Apr 17, 2025, 4:47 PM

                      @sdetweil – Thanks for the reminder, I’ll take a look.

                      1 Reply Last reply Reply Quote 0
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